CFD_Lecture_(Introduction_to_CFD)-CFD经典ppt

IntroductiontoComputationalFluidDynamics(CFD)TaoXing,ShantiBhushanandFredSternIIHR—Hydroscience&EngineeringC.MaxwellStanleyHydraulicsLaboratoryTheUniversityofIowa57:020MechanicsofFluidsandTransportProcesses~fluids/Ocrtober7,20092Outline1.What,whyandwhereofCFD?2.Modeling3.Numericalmethods4.TypesofCFDcodes5.CFDEducationalInterface6.CFDProcess7.ExampleofCFDProcess8.57:020CFDLabs3WhatisCFD?•CFDisthesimulationoffluidsengineeringsystemsusingmodeling(mathematicalphysicalproblemformulation)andnumericalmethods(discretizationmethods,solvers,numericalparameters,andgridgenerations,etc.)•HistoricallyonlyAnalyticalFluidDynamics(AFD)andExperimentalFluidDynamics(EFD).•CFDmadepossiblebytheadventofdigitalcomputerandadvancingwithimprovementsofcomputerresources(500flops,194720teraflops,20031.3pentaflops,RoadrunneratLasAlamosNationalLab,2009.)4WhyuseCFD?•AnalysisandDesign1.Simulation-baseddesigninsteadof“build&test”MorecosteffectiveandmorerapidthanEFDCFDprovideshigh-fidelitydatabasefordiagnosingflowfield2.SimulationofphysicalfluidphenomenathataredifficultforexperimentsFullscalesimulations(e.g.,shipsandairplanes)Environmentaleffects(wind,weather,etc.)Hazards(e.g.,explosions,radiation,pollution)Physics(e.g.,planetaryboundarylayer,stellarevolution)•Knowledgeandexplorationofflowphysics5WhereisCFDused?•WhereisCFDused?•Aerospace•Automotive•Biomedical•ChemicalProcessing•HVAC•Hydraulics•Marine•Oil&Gas•PowerGeneration•SportsF18StoreSeparationTemperatureandnaturalconvectioncurrentsintheeyefollowinglaserheating.AerospaceAutomotiveBiomedical6WhereisCFDused?Polymerizationreactorvessel-predictionofflowseparationandresidencetimeeffects.Streamlinesforworkstationventilation•WhereisCFDused?•Aerospacee•Automotive•Biomedical•ChemicalProcessing•HVAC•Hydraulics•Marine•Oil&Gas•PowerGeneration•SportsHVACChemicalProcessingHydraulics7WhereisCFDused?•WhereisCFDused?•Aerospace•Automotive•Biomedical•ChemicalProcessing•HVAC•Hydraulics•Marine•Oil&Gas•PowerGeneration•SportsFlowoflubricatingmudoverdrillbitFlowaroundcoolingtowersMarine(movie)Oil&GasSportsPowerGeneration8Modeling•Modelingisthemathematicalphysicsproblemformulationintermsofacontinuousinitialboundaryvalueproblem(IBVP)•IBVPisintheformofPartialDifferentialEquations(PDEs)withappropriateboundaryconditionsandinitialconditions.•Modelingincludes:1.Geometryanddomain2.Coordinates3.Governingequations4.Flowconditions5.Initialandboundaryconditions6.Selectionofmodelsfordifferentapplications9Modeling(geometryanddomain)•Simplegeometriescanbeeasilycreatedbyfewgeometricparameters(e.g.circularpipe)•Complexgeometriesmustbecreatedbythepartialdifferentialequationsorimportingthedatabaseofthegeometry(e.g.airfoil)intocommercialsoftware•Domain:sizeandshape•Typicalapproaches•Geometryapproximation•CAD/CAEintegration:useofindustrystandardssuchasParasolid,ACIS,STEP,orIGES,etc.•Thethreecoordinates:Cartesiansystem(x,y,z),cylindricalsystem(r,θ,z),andsphericalsystem(r,θ,Φ)shouldbeappropriatelychosenforabetterresolutionofthegeometry(e.g.cylindricalforcircularpipe).10Modeling(coordinates)xyzxyzxyz(r,,z)zr(r,,)r(x,y,z)CartesianCylindricalSphericalGeneralCurvilinearCoordinatesGeneralorthogonalCoordinates11Modeling(governingequations)•Navier-Stokesequations(3DinCartesiancoordinates)222222ˆzuyuxuxpzuwyuvxuutu222222ˆzvyvxvypzvwyvvxvutv0zwyvxutRTpLvppDtDRDtRDR222)(23ConvectionPiezometricpressuregradientViscoustermsLocalaccelerationContinuityequationEquationofstateRayleighEquation222222ˆzwywxwzpzwwywvxwutw12Modeling(flowconditions)•Basedonthephysicsofthefluidsphenomena,CFDcanbedistinguishedintodifferentcategoriesusingdifferentcriteria•Viscousvs.inviscid(Re)•Externalfloworinternalflow(wallboundedornot)•Turbulentvs.laminar(Re)•Incompressiblevs.compressible(Ma)•Single-vs.multi-phase(Ca)•Thermal/densityeffects(Pr,g,Gr,Ec)•Free-surfaceflow(Fr)andsurfacetension(We)•Chemicalreactionsandcombustion(Pe,Da)•etc…13Modeling(initialconditions)•Initialconditions(ICS,steady/unsteadyflows)•ICsshouldnotaffectfinalresultsandonlyaffectconvergencepath,i.e.numberofiterations(steady)ortimesteps(unsteady)needtoreachconvergedsolutions.•Morereasonableguesscanspeeduptheconvergence•Forcomplicatedunsteadyflowproblems,CFDcodesareusuallyruninthesteadymodeforafewiterationsforgettingabetterinitialconditions14Modeling(boundaryconditions)•Boundaryconditions:No-sliporslip-freeonwalls,periodic,inlet(velocityinlet,massflowrate,constantpressure,etc.),outlet(constantpressure,velocityconvective,numericalbeach,zero-gradient),andnon-reflecting(forcompressibleflows,suchasacoustics),etc.No-slipwalls:u=0,v=0v=0,dp/dr=0,du/dr=0Inlet,u=c,v=0Outlet,p=cPeriodicboundaryconditioninspanwisedirectionofanairfoilorxAxisymmetric15Modeling(selectionofmodels)•CFDcodestypicallydesignedforsolvingcertainfluidphenomenonbyapplyingdifferentmodels•Viscousvs.inviscid(Re)•Turbulentvs.laminar(Re,Turbulentmodels)•Incompressiblevs.c